The present invention relates to a method for the light-induced scanning-microscope display of a plurality of specimen parameters and of their distribution, as well as to apparatus for carrying out this method.
Various methods of analysis, optimalized for specific applications (chromatography, mass-spectrometry) which do not permit non-destructive measurement, are used at the present time for reliable specimen analysis.
With the spectral-photometric methods of analysis known up to the present time, however, the specimen to be examined cannot always be unequivocally identified, since involved weakly structured absorption spectra do not have any particularly great informational content. In particular, difficulties result when the specimen contains several substances having overlapping spectra. With known methods of optical analysis, one generally obtains merely integral information concerning the samples to be examined; nothing can be said with regard to the relative distribution of their parameters.
In the "Mikroprobe Mole" prospectus of Jobin Yvon Company and in GIT journal Laboratorium I, 1978, page 38, a method is described for the microanalytic examination of specimens in which they are continuously irradiated with laser light and observed in the light of their emitted Raman radiation. It is possible to use only light of characteristic Raman lines of given substances contained in the examined specimen, the relative distribution of which substances is to be determined. Depending on the adjustment of the monochromator used for observation, it is possible to produce substance-specific images of the specimen which are also informative as to the molecular structure of the components.
The sensitivity of this method is, to be sure, limited, since a laser of fixed wavelength is used to illuminate the entire region of the specimen; thus, high suppression of scattered light is necessary. Fluorescing specimen regions further reduce the sensitivity of the apparatus.
Furthermore, since the entire image of the surface of the specimen is transmitted through the monochromator, the obtainable resolution is limited.
In the particular case of lengthy short-wave light irradiation of sensitive specimens, damage to the object cannot be prevented. In actual use, this method is limited to specimens which supply a sufficiently intensive characteristic Raman spectrum. However, this is true only for molecules in which molecular vibration results in a significant change in polarizability.
In Journal of Raman Spectroscopy, No. 3 (1975), pages 33 to 43, mention is made of an arrangement for Raman microscopy which relies on laser-beam unidimensional scanning of a specimen moved perpendicular to the scanning direction, and electronic creation of the image is based on photo-multiplier signals selected in phase with the scanning frequency. Through raster-like scanning of the specimen one obtains, in light of the characteristic Raman radiation, specimen images which are of high definition, thereby obtaining greater sensitivity than in methods in which the entire surface to be examined is illuminated. Radiation damage to the material, which might occur, for example, in the case of geological specimens is minimized with raster-like scanning. The aforementioned sensitivity problems caused by fluorescent light, however, also occur with this known arrangement, since in both cases an entire scanning line is focused on the photo-multiplier.